Power-operated hammer

ABSTRACT

A power-operated hammer has a fluid-pressure piston and cylinder arrangement for generating the working impulses. The top of the piston fits an upper part of the cylinder to seal off a space such that the volume of the sealed space increases as the piston makes a return movement and a partial vacuum is created so that the resultant air pressure acting on the piston accelerates the reversal of its movement and increases the cycle frequency.

O United States Patent [191 [111 3,734,206 Last [4 1 May 22, 1973 541POWER-OPERATED HAMMER [56] References Cited [75] Inventor: AnthonyEdward Walter Last, Stow- UNITED STATES PATENTS market, England2,230,181 1 1941 C d t l. ..l23 46 [73] Assignee: The British SteelPiling Company I or es 8 a Limited Ipswlch Suffolk England PrimaryExaminer-Ernest R. Purser [22] Filed: Apr. 29, 1971 Attorney-Larson,Taylor & Hinds 21 A 1. No.: 138439 1 pp 57 ABSTRACT A power-operatedhammer has a fluid-pressure piston [30] Foreign Application PriorityData and cylinder arrangement for generating the working May 4, 1970Great Britain ..21,277/70 us. Cl .113/137, 123/46 Int. Cl. ..E02d 7/12Field ofSearch ..l73/l34137, 119-121;

12 Claims, 3 Drawing Figures POWER-OPERATED HAMMER This inventionrelates to power-operated hammers, for example for rock-breaking and forpile driving.

In order to increase the rate of working in conventional hammers, it isknown to provide a resilient return arrangement provided to act upon thereciprocating tool member to accelerate its return movement after aworking stroke producing the hammer impact. Thus, in previous designs ofdiesel-powered hammers, the diesel piston has had its upper end movingin a closed cylinder that thereby acts as an air spring when the airwithin it is compressed with the upward movement of the piston.

Although such an accelerated return of the piston can produce a markedincrease in the cycle frequency it is possible, and is especiallyapparent in general in diesel-powered hammers, that reaction forces ofthe resilient return means tend to lift the hammer, which is to beavoided, and when the hammer is arranged to act downwardly, as in a piledriver, it is usually necessary to make the cylinder constructionrelatively massive in order to prevent this from occurring.

According to the present invention, in a poweroperated hammer comprisinga piston reciprocable to produce a series of working impacts, the pistonprojects into an enclosure that forms, with the surface of a part of thepiston, a sealed space the volume of which increases with the returnmovement of the piston from a working impact, the arrangement being suchthat a suction force is developed that acts upon the said part of thepiston surface in the opposite direction to said return movement.

It is found that, by using such an arrangement, the peak pressure forceacting to accelerate the return motion of the piston is significantlyreduced, since it is limited by the value of atmospheric pressure if thespace beyond the piston is freely open to atmosphere, and in a hammerarranged for downwards driving the tendency to lift the hammer cylinderis correspondingly reduced. At the same time, the suction force is builtup relatively quickly as the piston rises so that despite the reductionin peak force a similar increase of cycle frequency can be achieved aswhen using a compression air spring.

Preferably the piston is mounted in a casing comprising a first portionproviding a space for pressure fluid to generate the working impacts,and a second portion in which said enclosed space is formed.Conveniently said first and second casing portions have differentdiameters, the piston being a unitary member having different diameterportions closely fitting the respective casing portions, when it can bearranged that the smaller diameter portions of the casing and pistoncooperate to provide said working fluid space and the piston smallerdiameter portion projects into the casing larger diameter portionwhereby said sealed space is formed in an annular region therebetweenand is closed by the piston larger diameter portion.

Advantageously, means are provided to open the sealed space toatmosphere at or near the beginning of said return movement of thepiston, or relief valve means are provided to limit the pressure in saidsealed space. Such a provision can prevent the generation of anysignificant positive gauge pressure in that space as the piston reachesthe bottom of its stroke if there has been any leakage into the spacewhile the piston was in a higher position and while a negative gaugepressure prevailed in the space.

By way of example only, a diesel-powered hammer according to theinvention will now be described in greater detail with reference to theaccompanying drawings of which:

FIG. 1 is a side view, in vertical section, of the lower region of thehammer, and

FIGS. 2 and 3 are side views, in vertical section of two alternativearrangements of the upper region of the hammer of FIG. 1.

Referring to the drawings, the hammer casing comprises a lower,cylindrical portion 2 and an upper, larger diameter cylindrical portion4 secured to it. Slidably mounted in the lower end of the portion 4 andsealing that end is an anvil block 6. A piston 8 is reciprocable withinthe casing from a lowermost position illustrated in FIG. 1 by acompression ignition cycle being operated in the combustion spacebetween the bottom of the piston and the casing portion 2. The piston 8,which may be of cast iron, has an integrally formed impact stem 10slidable in and sealing with the portion 2 of casing, and an enlargeddiameter head 12 located in. and sealing with the portion 4 of thecasing. Secured to the lower end of the hammer casing are pile grips 14,to attach a pile P and hammer together with a pile dolly 16 sandwichedbetween the anvil block 6 and the pile.

The upper face of the anvil block 6 and the lower face of the pistonstem 10 have opposed central cavities 18 while the outer region of thesefaces have complementary profiles sloping downwards towards the centralcavities. Fuel is injected from a pump in a casing 20 on to the anvilsloping face, the fuel following the trajectory 22. The supply to thepump is from a fuel tank 24 on the upper portion 4 of the casing.

The fuel pump is operated with the reciprocation of the piston 8 by acam 26 having spaced pivot connections to the casing lower portion andto rod 28 carrying a piston of the pump. The cam is spring-loaded toproject through a slot 30 in the casing wall and bear against the pistonstem 10. As the piston stem rises clear the slot, the cam moves inwardsto draw fuel into the pump and when the piston stem next descends, itstrikes the curved face of the cam and so displaces the rod 28 to injectthefuel through the line 22 into the combustion space. The injection isat low pressure since at this stage exhaust ports 34 (only one of whichis shown) are not yet covered by the piston stem 10.

The piston head 12 forms, with a. spring sealing ring 36 located at thejunction between the upper and lower casing portions, an enclosed space38 that is joined to the space above the piston, when the piston is inits lowermost position, by a channel 40, the function of which will bedescribed below.

, The top end of the casing portion 4 is open to atmosphere. Each timethe piston 8 rises after ignition of fuel injected with the casing belowit, the space 38 is sealed off once the piston head 12 has covered theupper end of the channel 40, and further upwards movement of the pistonthen increases the volume of the space 38 below the piston, with aconsequent reduction in pressure within this space. Hence, as a resultof the fact that the space is substantially sealed from its surroundingsduring at least a major portion of its increase in volume, a suctioneffect is set up on the base of the piston head 12 which tends to reducethe rise in the piston, the suction force increasing as the volume ofthe space 38 increases with the rise of the piston. The maximum suctionpressure is of course dictated by atmospheric pressure so that themaximum reactive force lifting the casing is always less than that dueto atmospheric pressure on the flange 2a of the portion 2 of the casingbelow the sealing ring.

Once the piston begins its downwards compression stroke thegravitational force on the ram is supplemented by the downward suctionforce in the increased volume of the space 38, and the ram isaccordingly accelerated by both forces, the latter force decreasing withdecrease in volume of the space 38.

Since there can be expected to be some leakage of air into the space 38while it is held at a negative gauge pressure, the pressure in the spacewould, without the channel 40, exceed atmospheric by a small amount atthe end of he downward stroke. By interconnecting the space 38 throughthe channel 40 with the open upper end of the casing as the piston nearsthe bottom of its stroke, it is possible to ensure that this pressure isnever in fact greater than atmospheric. An alternative way of achievingthis effect would be to connect the bottom of the space 38 directly toatmosphere through a nonreturn relief valve (as indicated at 42 in FIG.3) arranged to open when the internal pressure exceeds atmospheric.

In order to start the operation of the hammer, in the arrangementillustrated in FIG. 2, the piston 8 has a central cylindrical bore 44into which projects a rod 46 carrying a terminal enlargement 48. The rod46 extends the length of the portion 4 of the casing and has attached toits other end a suspension eye 50. The upper end of the bore 2 has atubular plug 52 of diameter less than that of the enlargement 48 so thatan abutment surface is presented to the enlargement when the rod 46 israised and the piston 8 can thus be lifted to an uppermost position andthen allowed to drop to start operation of the hammer.

An alternative starting arrangement shown in FIG. 3 employs a similarpiston with a plug 52 secured to the upper end of its bore. A tube 54 isfixed to the top of the casing in this case and is a free sliding fit inthe plug 52. A rod 56 with a suspension eye 58 attached to its upper endhas an engagement linkage at its lower end comprising an abutment member60 pivoted to the rod and joined to a hook member 62 by a pivot link 64.Both the abutment and hook members project through an elongate slot 66in the tube 54. When the rod is lifted by the suspension eye, the member60 engages the plug and the piston is then drawn up with the rod. Thewidth of the slot is reduced in its upper region and the hook member 62is made rather wider than the abutment member 60 so that as it reachesthis region it is restrained and is pivoted inwards, the connecting link64 being drawn downwards thereby to pivot the engagement member inwardsalso. As a result, the piston plug is no longer held by the engagementelement and the piston is allowed to fall. The mechanism is reset to theillustrated position by lowering the rod 56 until the hook member 62abuts pin 68, the weight of the rod then urging the engagement and hookmembers outwards and swinging the link 64 back past its overcenterposition.

This alternative arrangement has the advantage that it is not necessaryto lift the piston with a winch that has a free-fall pay-out mechanismsince the rod 56 need not fall with the piston.

In order to lubricate the hammer, the casing containing the fuel pumphas a separate cylinder space for the pumping of lubricating fluid, thisflow being actuated by a further shoulder or piston head on the samepiston rod 28. From the lubricating pump oil is directed, firstly, intothe upper casing portion 4 for lubrication of the rings of the pistonhead 12, secondly into the lower casing portion 2 for lubrication of therings of the piston stem 10, and thirdly to the outer circumference ofthe anvil block 6 for lubrication of this block in its sliding contactwith the casing.

While only a diesel-powered hammer has been illustrated in the foregoingdescription it will be understood that the invention can be applied tohammers having other driving means, for example, compressed air, in anentirely analogous manner and no further description is thereforenecessary. It will also be apparent that the invention can be applied tohammers arranged for operations other than pile-driving, as for examplerock breaking.

What we claim and desire to secure by Letters Patent l. A power-operatedhammer comprising, in combination, a casing, a piston reciprocable inthe casing to produce a series of working impacts, an enclosure formedbetween the casing and a projecting part of the piston, said enclosurebeing partly bounded by the surface of a part of the piston to define anenclosed space the volume of which increases with the return movement ofthe piston from a working impact, the enclosed space being substantiallysealed from its surroundings during at least a major portion of itsincrease in volume such that a suction force is developed during suchportion of its increase in volume that acts upon the said part of thepiston surface in the opposite direction to said return movement.

2. A hammer according to claim 1 wherein means are provided to open theenclosed space to atmosphere at or near the beginning of said returnmovement of the piston.

3. A hammer according to claim 1 wherein relief valve means are providedto limit the pressure in said enclosed space.

4. A hammer according to claim 1 wherein the casing comprises a firstportion providing a space for pressure fluid to generate the workingimpacts, and a second portion in which said enclosed space is formed.

5. A hammer according to claim 4 wherein said first and second casingportions have different diameters, different diameter portions of aunitary piston closely fitting the respective casing portions.

6. A hammer according to claim 5 wherein the smaller diameter portionsof the casing and piston cooperate to provide said working fluid spaceand the piston smaller diameter portion projects into the casing largerdiameter portion whereby said enclosed space is formed in an annularregion therebetween and is closed by the piston larger diameter portion.

7. A hammer according to claim 6 further comprising means in said secondcasing portion arranged to bring the regions on opposite sides of thelarger diameter piston portion in communication with each other at ornear the beginning of said return movement of the piston.

8. A hammer according to claim 1 arranged for diesel operation, aworking fluid space between the casing and the piston forming acombustion chamber and being disposed in a lower region of the hammer, amember underneath the hammer being arranged to receive the workingimpacts.

9. A hammer according to claim 8 wherein a hollow core is provided inthe piston, lifting means being in sertable into said hollow core toengage and lift the piston for starting operation of the hammer.

10. A hammer according to claim 9 wherein the lifting means comprises asuspended engagement element, a restriction at the upper end of saidcore being engageable with said element to allow the piston to be liftedtherewith.

11. A hammer according to claim 10 wherein means are provided to retractsaid engagement element at a predetermined raised position of the pistonto release the piston and allow it to fall.

12. A diesel-powered hammer comprising, in combination, a casing havinga cylindrical lower portion providing the combustion space and a largercross-section upper portion, a piston reciprocable in the casing havinga lower portion forming an upper boundary of the combustion space, anenlarged head of the piston sealingly fitting said casing upper portionand defining therewith an enclosed space, an underface of said pis tonhead forming an upper boundary of said enclosed space, the volume ofsaid enclosed space increasing with the increase of volume of thecombustion space, the enclosed space being substantially sealed from itssurroundings during at least a major portion of its increase in volumesuch that, as the piston rises in the casing, a suction force isdeveloped acting on said underface to accelerate the return of thepiston in a downwards working stroke.

1. A power-operated hammer comprising, in combination, a casing, apiston reciprocable in the casing to produce a series of workingimpacts, an enclosure formed between the casing and a projecting part ofthe piston, said enclosure being partly bounded by the surface of a partof the piston to define an enclosed space the volume of which increaseswith the return movement of the piston from a working impact, theenclosed space being substantially sealed from its surroundings duringat least a major portion of its increase in volume such that a suctionforce is developed during such portion of its increase in volume thatacts upon the said part of the piston surface in the opposite directionto said return movement.
 2. A hammer according to claim 1 wherein meansare provided to open the enclosed space to atmosphere at or near thebeginning of said return movement of the piston.
 3. A hammer accordingto claim 1 wherein relief valve means are provided to limit the pressurein said enclosed space.
 4. A hammer according to claim 1 wherein thecasing comprises a first portion providing a space for pressure fluid togenerate the working impacts, and a second portion in which saidenclosed space is formed.
 5. A hammer according to claim 4 wherein saidfirst and second casing portions have different diameters, differentdiameter portions of a unitary piston closely fitting the respectivecasing portions.
 6. A hammer according to claim 5 wherein the smallerdiameter portions of the casing and piston co-operate to provide saidworking fluid space and the piston smaller diameter portion projectsinto the casing larger diameter portion whereby said enclosed space isformed in an annular region therebetween and is closed by the pistonlarger diameter portion.
 7. A hammer according to claim 6 furthercomprising means in said second casing portion arranged to bring theregions on opposite sides of the larger diameter piston portion incommunication with each other at or near the beginning of said returnmovement of the piston.
 8. A hammer according to claim 1 arranged fordiesel operation, a working fluid space between the casing and thepiston forming a combustion chamber and being disposed in a lower regionof the hammer, a member underneath the hammer being arranged to receivethe working impacts.
 9. A hammer according to claim 8 wherein a hollowcore is provided in the piston, lifting means being insertable into saidhollow core to engage and lift the piston for starting operation of thehammer.
 10. A hammer according to claim 9 wherein the lifting meanscomprises a suspended engagement element, a restriction at the upper endof said core being engageable with said element to allow the piston tobe lifted therewith.
 11. A hammer according to claim 10 wherein meansare provided to retract said engagement element at a predeterminedraised position of the piston to release the piston and allow it tofall.
 12. A diesel-powered hammer comprising, in combination, a casinghaving a cylindrical lower portion providing the combustion space and alarger cross-section upper portion, a piston reciprocable in the casinghaving a lower portion forming an upper boundary of the combustionspace, an enlarged head of the piston sealingly fitting said casingupper portion and defining therewith an enclosed space, an underface ofsaid piston head forming an upper boundary of said enclosed space, thevolume of said enclosed space increasing with the increase of volume ofthe combustion space, the enclosed space being substantially sealed fromits surroundings during at least a major portion of its increase involume such that, as the piston rises In the casing, a suction force isdeveloped acting on said underface to accelerate the return of thepiston in a downwards working stroke.